Endocrine and Nervous System Flashcards
The two parts of the nervous system
Central Nervous System
- Brain and spinal cord
- Control centre
Peripheral Nervous System
- Nerve cells, receptors
- Carry messages to and from CNS
Functional Types of Neurons
- Sensory
- carry messages from receptors in sense organs towards CNS - Motor
- Carry messages away from CNS - Interneuron
- Link between sensory and motor neurones in the CNS
Structural types of Neurons
- Multipolar
- Bipolar
- Unipolar
- Pesudounipolar
Conduction along myelinated fibres
In unmyelinated fibres, depolarisation of one area of the membrane causes another repolarization immediately next to the original stimulus
This process repeats along the whole membrane, moving away from the original stimulus, from one channel to the next
The nerve impulse is prevented from going backwards by the refractory period
Conduction along myelinated fibres
In myelinated fibres, the nerve fibres are insulated from the extracellular fluid by schwann cells
Ions cannot flow where the fibre is insulated so no action potential can occur, except at the nodes of ranvier
Sodium ions will diffuse along axon through the cytoplasm until they reach the next exposed gate (node of ranvier), the action potentials are said to jump from one node to another
With action potentials only occurring at the nodes of ranvier, there is less distance to cover = much faster
Conduction along a myelinated axon is also called saltatory conduction
Synapses
- Nerve impulse reaches axon terminal which activates voltage-gated ion channels in presynaptic membrane
- Calcium ions flow into the presynaptic axon terminal
- This stimulates the release of chemicals called neurotransmitters from vesicles by exocytosis at the presynaptic membrane
- The neurotransmitters diffuse across the synaptic cleft and attach to receptors on the postsynaptic membrane
- This stimulates ligand-gated protein channels to open, which allows an influx of sodium ions into the dendrite, initiating a nerve impulse in the next neuron
Examples of Neurotransmitters
→ Acetylcholine → Noradrenaline → Dopamine → Histamine → Serotonin
Removal of Neurotransmitters
Diffusion
→ Neurotransmitters exit the synaptic cleft via diffusion as they move from a high to a lower concentration
Enzymes degradation
→ Enzymes can inactivate the neurotransmitter, these are released by the postsynaptic membrane when the neurotransmitter has been received
Active reabsorption
→ Reabsorbed back into the presynaptic axon terminal by active transport
In the intracellular and extracellular fluids the concentrations are:
→ Extracellular fluid has a high concentration of sodium ions and chlorine ions
→ Intracellular fluid has a high concentration of potassium ions and various negative ions and low concentrations of sodium and chlorine ions
The cell membrane is:
Highly permeable to potassium ions
Slightly permeable to sodium ions
Impermeable to large negative ions
→ Therefore there is a tendency for potassium ions to diffuse out of the cell, this makes the cell more negatively charged as its losing positive ions
The potential difference created is called the membrane potential
The resting membrane potential is the membrane potential/difference of unstimulated nerve cells
> -70 mV (millivolts) - This means the potential of the inside of the membrane is 70mV less than that of outside
Maintaining the potential difference in two ways
- Sodium potassium pump
→ Cell activity moves sodium ions out of the cell and potassium ions into the cell using sodium and potassium protein pumps, for every 3 sodium ion molecules released, 2 potassium ion molecules will be brought back - Cell membrane is not equally permeable to all ions which means many negatively charged ions are trapped inside the cell
Action Potential
When a sufficiently strong stimulus is applied to a nerve fibre, the membrane will become more permeable to sodium ions therefore sodium channels will open and diffuse into cell
→ This enables cell to be more positive inside than the outside and increases the potential difference
If the level of stimulation exceeds 15mV (-70 to -55) it is known as an All or None response and can be passed along axon
→ When it exceeds 15mV it is classified as a sufficiently strong stimulus
→ Doesn’t matter size of impulse, if above 15 it will go if it doesn’t nothing will happen
→ ‘passed along axon’ is known as the action potential
The movement of sodium ions is independent to the strength of the stimulus
The flood of sodium ions into the cell causes the inside of the cell to reach a charge of 0 and slightly positive → Depolarisation/switching of charges
To re-polarize the cell, the sodium channels close and potassium ions diffuse out of cell therefore potassium ions open to return and create a negative charge
When potassium channels remain open for longer what is needed the potential drops lower than the resting → hyperpolarized
The rapid depolarisation and repolarisation is called the action potential
The movement of an action potential along a nerve is known as the nerve impulse
Nervous system divides into two divisions
Central nervous system
Peripheral nervous system
Central nervous sytem
Brain and spinal cord
Peripheral nervous system
Nerves, receptors and effectors
Peripheral nervous system divides into two divisions
Afferent: carries into to CNS from receptors
Efferent: carries info away from CNS to effectors
Afferent division
- Somatic: carry info from receptors in skin, muscles or joints
- Visceral: Carry info from receptors in internal organs
Efferent division
- Somatic: carry info to skeletal muscles
2. Autonomic: Carry info to involuntary muscles and glands
Autonomic divisions
Parasympathetic: rest and digest
Sympathetic: fight or flight
What is a receptor
Detects changes in the body’s internal or external environment
Thermoreceptors purpose
Detect temperatures
Thermoreceptors location
Skin - detect external temp
Hypothalamus - detect internal temp
Thermoreceptors function
Hypothalamus collects information which can regulated body temperature
Osmoreceptors purpose
Detect osmotic pressure
Osmoreceptors location
Hypothalamus
Osmoreceptors function
Stimulate the posterior pituitary to release ADH to regulate osmotic pressure
Chemoreceptors purpose
Detects chemicals
Chemoreceptors location
Nose and mouth and internally
Chemoreceptors function
Receptors detect composition of body fluids (pH, O2 and CO2) and these messages are sent to the respiratory centre to regulate breathing rate
Touch receptors purpose
Detect touch
Touch receptors location
mostly in the skin
Touch receptors function
Detect light touches and harder touches and these messages are sent to the brain to give response
Pain receptors prupose
Detect pain
Pain receptors location
Skin and mucous membrane
Pain receptors function
Stimulated by damage to tissues, excessive heat or chemicals and messages are sent to brain to detect pain
Describe the Cerebrum
Many convolutions which increases surface area
Separated by shallow folds called sucli or deep folds called fissures
Deepest fissure - longitudinal fissure which separates brain into right and left hemisphere
4 lobes of brain
Frontal
Temporal
Occipital
Parietal
Frontal lobe
Important for voluntary movement, expressive language and for managing higher level executive function
Occipital Lobe
The occipital lobe is the visual processing area of the brain. It is associated with visuospatial processing, distance and depth perception, colour determination, object and face recognition, and memory formation
Temporal lobe
important role in processing affect/emotions, language, and certain aspects of visual perception
Parietal lobe
Processes sensory information it receives from the outside world, mainly relating to touch, taste, and temperature
Cerebral cortex matter
Grey
Tracts
White matter
Types of tracts
Connect various areas in the same hemisphere
Carry impulses between hemispheres
Connect to other parts of brain or spinal cord
Basal ganglia
Underneath the tracts, grey matter
Functional areas of the brain
- Sensory areas
- Motor areas
- Association areas
Sensory areas
Interpret impulses from receptors, perception of sense
Motor areas
Control muscular movements, initiation and control of voluntary muscle
Association areas
Intellectual and emotional processes, involved in activities such as thinking, reasoning, learning, memory
Corpus Callosum
Wide band of nerve fibres underneath the cerebrum
Enables both hemispheres to communicated
Cerebellum Location
Back of the cerebrum
Role of Cerebellum
Receives constant input from the senses
Maintains muscles tone and posture
Hypothalamus location
Located in middle of brain
Hypothalamus function
Controls homeostasis
Body temperatures
Autonomic nervous system
Medulla Olbongata
- Cardiac centre - regulated rate and force of heartbeat
- Respiratory centre - control of rate and depth of breathing
- Vasomotor centre - regulated diameter of blood vessels
Protection of CNS - Bone
Hardness of the cranium encases the brain
Protection of CNS - Meninges
- Dura mater - tough fibrous, prevents brain from moving around
- Arachnoid mater - loose mesh fibres
- Pia mater - creates a seal that protect brain from infection
Cerebrospinal fluid properties
Clear watery fluid, contains glucose, protein, urea and salta
Functions of cerebrospinal fluid
Protection - shock absorber
Support - brain is suspended in cranium
Transport - takes nutrients to cells and wastes away
Reflex
Triggered by a stimulus
Involuntary
Rapid
Stereotypes
Reflex arc
- Receptor in the end of a sensory neuron detect a change in the environment and reacts to this stimulus by producing a nerve impulse
- Sensory neuron carries impulse to spinal cord
- Information is processed in CNS, nerve impulse is passed across a synapse to a motor neuron via an interneuron
- Motor neuron then carries nerve impulse to an effector
- The effector receives nerve impulse and carries out an appropriate response
Protective reflexes
Blinking
Sneezing
Coughing
Exocrine Glands
Secrete into a duct that carries the secretion to the body surface
Endocrine glands
Secrete hormones into the extracellular fluid that surrounds the cells making up the gland
Pituitary gland
Lies just underneath the hypothalamus and is joined by the stalk called the infundibulum
Has two lobes
Anterior lobe
Connected to the hypothalamus via blood vessels
Produces own hormones
Releases hormones via chemical stimulation
Posterior lobe
Connected to hypothalamus by nerve fibres
Releases hormones from hypothalamus
Releases hormones via nervous stimulation
Transmission of hormones from the posterior lobe
- Hormones transport down the axons of the nerve cells to the posterior lobe
- There are stored in the posterior lobe until required
- Their release is triggered by a nervous impulse which is initiated by the hypothalamus and conducted along the nerve cell extensions
Hormones
Change functioning of cells by changing the type, activities or quantities of proteins produced
Hormones Functions
Activate certain genes so that a particular enzyme or protein produced
Change the shape or structure of an enzyme
Change the rate of production of an enzyme or protein
Protein and Amine hormones
- Attach to receptors on surface of cell membrane of target cell
- This combination of hormone and receptor causes a secondary messenger to diffuse through the cell and activate particular enzymes within the cytoplasm
- Faster acting hormones
Steroid hormones
- Enter target cells and combine with receptor protein inside the cytoplasm of cell
- Lipid soluble so easily diffuse through cell membrane
- The hormone-receptor complex then enters the nucleus and activates genes controlling formation of particular proteins
- Slower acting hormones
Anterior lobe Hormones
- Follicle Stimulating Hormone: Ovaries and testes : growth of follicles, production of sperm
- Luteinising hormone: ovaries and testes: ovulation and maintenance or corpus luteum and secretion of testosterone
- Growth hormone: all cells: growth and protein synthesis
- Thyroid-stimulating hormone: thyroid gland: secretion of hormones from the thyroid
- Adrenocorticotropic hormone: adrenal cortex: secretion of hormones from the adrenal cortex
- Prolactin: mammary glands: milk production
Posterior lobe
Antidiuretic hormone
- Kidneys: reabsorption
- Uterus: contractions of uterus during childbirth
Oxytocin
1. Mammary glands: release of milk
Thyroid
Thryoxine: Most body cells, increases metabolic rate, oxygen consumption and heat production
Calcitonin: bones, kidneys, decreases calcium and phosphate in the blood
Parathyroid
Parathyroid: bones and kidneys, increases level of calcium in blood
Thymus
Thymosis: T-lymphocytes, stimulates development and maturation of t-lymphotcytes
Adrenal cortex
- Corticosteroids: kidneys, increases reabsorption of sodium ions and excretion of potassium ions
- Cortisol: most body cells, promotes normal metabolism, helps body deal with stress, promotes damages tissues
Adrenal medulla
Adrenaline: most body tissues, prepares the body for fight or flight response
Pancreas
Insulin: most body cells, stimulates uptake of glucose, lowers blood glucose level
Glucagon: liver, stimulates breakdown of glycogen and fat
Testes
Androgens: many tissues, stimulate sperm production, growth of skeleton, development of male sexual characteristics
Ovaries
Oestrogen: many tissues, stimulate development of female sexual characteristics
Progesterone: uterus and mammary glands, regulates menstural cycle and pregnancy
Homeostasis
Maintenance of internal environment
Feedback system
The response causes the stimulus a direction opposite to that of the original stimulus
What does a feedback system consists of
- Stimulus
- Receptor
- Modulator
- Effector
- Feedback
Positive feedback
The response to stimulus reinforcer and intensifies the stimulus
Heat Gain Internal
Heat is a by-product of cellular respiration
Metabolic rate, which energy is released by the breakdown of food
Metabolic rate is affected by exercise, stress and body temperature
Heat Gain External
Radiation or conduction from surroundings
Heat Loss Internal
Evaporation of water from skin and lungs
Warm air breathed out
Warm urine and faeces
heat Loss External
Radiation
Conduction
Convection to surroundings
Conduction
Transfer of heat via direct contact with another object
Involves the exchange of heat from molecule of higher temperature to molecule of lower temperature when they vibrate and touch
Convection
Transfer to heat to air around the body
When cool air makes contact with our body it heats up and becomes less dense, less dense air rises and is replaced by cooler more dense air
Radiation
Transfer to heat without contact
All objects emit heat to their surroundings by radiation
Heat will radiate to cooler objects around you like the floor and walls
Evaporation
Transfer of heat through evaporation of liquid to gas
Heat energy is required to change from a lower energy liquid phase to a higher energy gas phase
This heat energy is absorbed from the surface of the skin, which then cools when the water evaporates, meaning heat is lost
Temperature tolerance
- Heat stroke, body temp rises by regulatory mechanisms are not working
- Heat exhaustion, result of extreme sweating and vasodilation
- Hypothermia, if cored body temp balls below 33 degrees
Temperature receptors
- Peripheral thermorecepotors skin and mucous membranes
